 Stereospecific Location of Fatty Acids and the Impact on Oxidation John Sullivan

Introduction  Interesterification  Lipid Oxidation  Oxidation and Stereospecific Location of Fatty Acids

Interesterification  Process where the fatty acids have been moved from one triglyceride molecule to another. Fatty acid redistribution within the triacylglycerol produces substantial changes in lipid functionality.  Process has become an alternative to partial hydrogenation to modify fats for use as margarines and shortening base stocks and reduce/exclude trans fatty acids.  Two methods for Interesterification:  Chemical  Enzymatic

Interesterification

Chemical Interesterification Pretreatment of Oil Reaction Catalyst NaOCH3 Deactivation (water/acid) BleachingDeodorization

Chemical Interesterification  Random Interesterification  Requires Soduim Methoxide as a Catalyst  Requires High Heat (50 – 120°C)  High Oil Loss  Loss of Tocophenols

Enzymatic Interesterification Pretreatment of Oil Reaction Catalyst (Lipase) Deodorization

Enzymatic Interesterification  Lipase Catalyzed  Immobilized Enzyme  Low Heat  Loss of Tocopherols  Selective Fatty Acid Interchange on sn-1,3 Position

Lipid Oxidation  Oil quality and shelf life are directly affected by Lipid Oxidation.  Oxidation of Oil  Destroys essential fatty acids  Produces off-flavor compounds and aromas  Produces toxic compounds

Mechanims of Lipid Oxidation  Auto-Oxidation  Initiated when a hydrogen atom is abstracted in the presence of initiators such as light, heat, metals and oxygen.  Forms a lipid radical that reacts with oxygen making a lipid peroxide radical  The lipid peroxide radical reacts with a second lipid yielding a lipid radical and a hydroperoxide  Photo-Oxidation  Normal triplet oxygen 3 O 2 (atmospheric oxygen) is converted to singlet oxygen 1 O 2 due to exposure to UV radiation  Singlet Oxygen interacts with polyunsaturated fatty acids to form hydroperoxide initiating the auto-oxidation reaction

Auto-Oxidation  Includes Three steps :  Initiation  Hydrogen atom in the fatty acid is removed and lipid alkyl radicals are produced  Propagation  The lipid alkyl radical reacts with 3 O 2 and forms lipid peroxy radical  The lipid peroxy radical abstracts hydrogen from other lipid molecules and reacts with the hydrogen to form hydroperoxide and another lipid alkyl radical  Termination  Radicals react with each other  Non-radical species are produced

Auto-Oxidation  The Hydroperoxides produced in Auto-Oxidation are primary oxidation products  These Hydroperoxides are decomposed to alkoxy radicals that then form secondary lipid oxidation products  Secondary oxidation products are mostly low-molecular weight aldehydes, ketones, alcohols and short chain hydrocarbons (responsible for off-flavors in oxidized oil)

Oxidation and Stereospecific Location of Fatty Acids  Challenges in Oxidation Stability:  Trying to produce functional lipids that include unsaturated fatty acids while avoiding the inclusion of trans -fats and synthetic antioxidants  Traditional methods of hydrogenation and partial hydrogenation are no longer viable options  Oils that are more unsaturated are oxidized quicker than less unsaturated oils

Oxidation and Stereospecific Location of Fatty Acids  Enzymatic Interesterification:  Utilizing sn -1,3 specific lipase results in the sn -2 fatty acids remaining conserved in an Interesterified Triacylglyceride.  This form of Interesterification can help protect long chain polyunsaturated fatty acids from being rapidly oxidized by securing them into the sn -2 position on the glycerol backbone.

Oxidation and Stereospecific Location of Fatty Acids  Docosahexaenoic Acid (DHA) Example:  DHA – long chain polyunsaturated fatty acid shown to play an important role in human health  Extremely high susceptibility to oxidative rancidity limits the product range of DHA-enriched foods  Stereospecific location of DHA sn -2 (PDP,ODO) compared to DHA sn- 1(3) (PPD,OOD) position in regard to oxidative stability. Where P=palmitic acid and O =oleic acid

Oxidation and Stereospecific Location of Fatty Acids  ODO/OOD and PDP/PPD Samples were oxidized and Peroxide Values (PV) were determined at 500nm using a spectrophotometric method.

Conclusion  The use of the Enzyme Interesterified sn -1,3 specific lipase process can help control the oxidation of long chain polyunsaturated fatty acids  Enzyme Interesterification also produces less free fatty acids, Mono- and Diacylglycerols, while retaining more Tocopherols as opposed to Chemical Interesterification

References  Chaiyasit, W., Elias, R. J., McClements, D. J., & Decker, E. A. (2007). Role of physical structures in bulk oils on lipid oxidation. Critical Reviews in Food Science & Nutrition, 47 (3), Retrieved from ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url= &site=eds-livehttp://p2048-lib- ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url= &site=eds-live  Choe, E., & Min, D. B. (2006). Mechanisms and factors for edible oil oxidation Retrieved from ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url= &site=eds-livehttp://p2048-lib- ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url= &site=eds-live  Ledochowska, E., & Eilczynska, E. (1998). Comparison of the oxidative stability of chemically and enzymatically interesterified fats Retrieved from ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url= &site=eds-livehttp://p2048-lib- ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url= &site=eds-live  Lee, K. T., & Akoh, C. C. (1998). Structured lipids: Synthesis and applications. Food Reviews International, (1) Retrieved from ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url= ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url=  Waraho, T., Decker, E. A., & McClements, D. J. (2011). Mechanisms of lipid oxidation in food dispersions [electronic resource]. Trends in Food Science & Technology, 22 (1), doi:  Wijesundera, C., Ceccato, C., Watkins, P., Fagan, P., Fraser, B., Thienthong, N., et al. (2008). Docosahexaenoic acid is more stable to oxidation when located at the sn-2 position of triacylglycerol compared to sn-1(3). Journal of the American Oil Chemists' Society, (6) Retrieved from ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url= ezproxy.tamu.edu.ezproxy.library.tamu.edu/login?url=  Yamamoto, Y., Imori, Y., & Hara, S. (2014). Oxidation behavior of triacylglycerol containing conjugated linolenic acids in sn-1(3) or sn-2 position. Journal of Oleo Science, 63 (1), doi: /jos.ess13129